The trend in the art of integrated circuit is for more products to be integrated higher. In the production of semiconductor substrates having ultrahigh LSI, it has been necessary to form an ultrafine pattern having a line width of not greater than quarter micron. As one of methods for enhancing the fineness of pattern there has been known a method involving the shifting of the wavelength of the exposing light source for use in the formation of resist pattern.
For the production of semiconductor elements having an integration degree of up to 64 megabits, i-ray (365 nm) from high voltage mercury vapor lamp has been heretofore used as a light source. As positive-working resist compositions adapted for this light source there have been developed many compositions comprising a novolac resin and a naphthoquinonediazide compound as a photosensitive material. With these compositions, satisfactory results have been attained for the formation of a line width of not smaller than about 0.3 μm. For the production of semiconductor elements having an integration degree of not smaller than 256 megabits, KrF excimer laser (248 nm) has been used as an exposing light source instead of i-ray.
Moreover, for the purpose of producing semiconductors having an integration degree of not smaller than 1 gigabits, the use of ArF excimer laser beam (193 nm), which is a short wavelength light source, has been studied. For the purpose of forming a pattern having a line width of not greater than 0.1 μm, the use of F2 excimer laser beam (157 nm) has been studied.
To cope with this trend for shorter wavelength of light source, the constituents of resist materials and their chemical structures have been drastically changed.
As a resist composition for exposure to KrF excimer laser beam there has been developed a composition comprising as a main component an acid decomposable group-protected resin having a poly (hydroxystyrene) having a small absorption at 248 nm as a basic skeleton in combination with a compound (photo-acid generator) which generates an acid when irradiated with far ultraviolet rays, i.e., so-called chemically-sensitized resist.
Further, as a resist composition for exposure to ArF excimer laser beam (193 nm) there has been developed a chemically-sensitized resist comprising an acid-decomposable resin having an alicyclic structure having no absorption at 193 nm incorporated in the polymer main chain or side chain.
Referring to F2 excimer laser beam (157 nm), it was found that even the aforementioned alicyclic resin exhibits a great absorption at 157 nm and thus leaves something to be desired in the provision of the desired pattern having a line width of not greater than 0.1 μm. On the other hand, it has been reported in Proc. SPIE. Vol. 3678, page 13, 1999, that a resin having fluorine atoms incorporated therein (perfluoro structure) has a sufficient transparency at 157 nm. Effective fluorine-containing resin structures are proposed in Proc. SPIE. Vol. 3999, page 330, 2000, page 357 (2000), and page (2000), WO-00/17712,etc. Studies have been made of resist compositions comprising fluorine-containing resin.
However, the resist composition comprising fluorine-containing resin for exposure to F2 excimer laser beam is disadvantageous in sensitivity and contrast. It has thus been desired to solve these problems.